Beppo-SAX Observations of Galaxy Clusters

The high spatial resolution of the MECS experiment on board Beppo-SAX has encouraged a few scientists, including the author, to perform observations of galaxy clusters. Results from the analysis of the first few observed objects are encouraging. After having reviewed the Beppo-SAX observing program for galaxy clusters and referenced contributions to these proceedings by other authors on the same topic, I present results from the analysis of the Perseus cluster.Comment: 4 pages, 4 Postscript figures included. To appear in the proceedings of the ``Active X-ray Sky: Results from BeppoSAX and Rossi-XTE'

First Beppo-SAX results on AGN

In the following paper, some first Beppo-SAX results on AGN are presented. Main on-flight calibration features and observational properties are discussed at the light of possible future AGN studiesComment: 5 pages, Latex, 4 Postscript figures, `an-art.sty' included, to appear in Astronomische Nachrichten, vol.4, pag. 22

Ion acceleration driven by intense laser pulses

Laser pulses incident on plasma targets are capable of exciting very intense accelerating fields, that allow the acceleration of ions to high energies in very short distances. This is why a lot of interest has been developed on the topic of laser-driven ion acceleration over the past twenty years. Such a compact and affordable ion source would have many potential applications in physics and medicine, but several requirements are still far from being fulfilled. In this thesis two mechanisms of ion acceleration are investigated: shock wave acceleration and Coulomb explosion. Ultraintense lasers shot on plasma targets are capable of driving strong electrostatic shock waves that accelerate the plasma ions to high energies with a narrow energy spectrum. In the present work, the mechanism of shock formation and propagation in near-critical density plasmas is studied in detail. An idealized scenario where shock waves arise from the interpenetration of plasma slabs is studied. A theoretical kinetic model is derived and compared with simulation results. The conditions to accelerate ions to high energies with low energy spread are derived. The role of the laser in exciting shock waves is analyzed. The factors leading to high energy ion beams with narrow energy spectrum obtained in the simpler configuration are verified in this more complex and realistic scenario. A scaling for the ion energy with the pulse intensity is inferred for the ideal case of a plane wave and for a more realistic case of a finite size laser spot. The second mechanism of ion acceleration that has been considered is the Coulomb explosion of pure ion nanoplasmas, an important subject in the field of laser-cluster interaction. In this thesis, a detailed study of Coulomb explosion in hetero-nuclear clusters consisting of different atomic species is carried out. Numerical results indicate that, in the presence of different ion species, lighter ions are accelerated in a quasi-monoenergetic way, in contrast with the well known results on Coulomb explosion of clusters composed by a single ion species, where the energy spectrum is much broader. A study on the formation of shock shells, nonlinear structures that arises during Coulomb explosion of homo-clusters when the initial density exhibits radial non-uniformity, is also presented. The analysis is carried out comparing N-body simulation results, that represent the exact solution since no approximations have been made, to the collisionless kinetic theory. The study shows that there are consistent differences between the real dynamics and the model based on the Vlasov-Poisson equations

Discovery of X-rays from the supernova remnant G0.9+0.1

During the $BeppoSAX$ survey of the Galactic Center region, we have discovered X-ray emission from the central region of the supernova remnant G0.9+0.1. The high interstellar absorption (N_H about 3 times 10^{23} cm^-2) is consistent with a distance of order of 10 kpc and, correspondingly, an X-ray luminosity of about 10^{35} erg s^{-1}. Although we cannot completely rule out a thermal origin of the X-ray emission, its small angular extent (radius of about 2'), the good fit with a power law, the presence of a flat spectrum radio core, and the estimated SNR age of a few thousand years, favour the interpretation in terms of synchrotron emission powered by a young, energetic pulsar.Comment: 4 pages, 1 figure. Uses espcrc2.sty (included). To appear in The Active X-ray Sky: Results from BeppoSAX and Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P. Giommi and F. Fiore (eds.), Elsevier Science B.

Timing, glitches and braking index of PSR B0540-69

We report a pulse-time history of PSR B0540$-$69 based on the analysis of an extended Data set including ASCA, BeppoSAX and RXTE observations spanning a time interval of about 8 years. This interval includes also the epoch of the glitch episode reported by Zhang et al. (2001). Our analysis shows the presence of a relevant timing noise and does not give a clear evidence of the glitch occurrence. We performed an accurate evaluation of the main timing parameters, $\nu$, $\dot{\nu}$ and $\ddot{\nu}$ and derived a mean braking index of $n=2.125\pm0.001$ quite different from the lower value found by Zhang et al. (2001), but in rather good agreement with other several values reported in the literature.Comment: 9 pages 5 figures, accepted by A&A, main journa

CMB Observations: improvements of the performance of correlation radiometers by signal modulation and synchronous detection

Observation of the fine structures (anisotropies, polarization, spectral distortions) of the Cosmic Microwave Background (CMB) is hampered by instabilities, 1/f noise and asymmetries of the radiometers used to carry on the measurements. Addition of modulation and synchronous detection allows to increase the overall stability and the noise rejection of the radiometers used for CMB studies. In this paper we discuss the advantages this technique has when we try to detect CMB polarization. The behaviour of a two channel correlation receiver to which phase modulation and synchronous detection have been added is examined. Practical formulae for evaluating the improvements are presented.Comment: 18 pages, 3 figures, New Astronomy accepte